The present invention is in the field of microelectromechanical systems (MEMS). More particularly, the present invention relates to a microcantilever. In one of its aspects, the present invention is directed to a microprobe which incorporates the microcantilever and which is used for high resolution material characterization. In another of its aspects, the present invention is directed to a conformable, high-pin count, programmable wafer probe (called a CHIPP probe card) which incorporates an array of the microcantilevers for device characterization.
Recently, a great deal of effort has been expended to develop electromechanical devices, such as sensors and actuators, on a microscopic scale. Many of the techniques developed over the years for silicon chip processing have been used to produce these microelectromechanical devices. These techniques include photolithography, X-ray and e-beam lithography, layer deposition and etching techniques, etc. For example, these techniques have been used to produce atomically sharp tips which can be used as electron emitters in microelectronic devices, or as mechanical, electrical, or magnetic microsensors or microprobes.
In an article by R. B. Marcus et al, appearing in Appl. Phys. Lett., 56(3), p. 236 (1990), a method is described for preparing uniform silicon tips having a radius of curvature of less than 1 nm. The process described therein involves producing silicon cones by isotropic etch, followed by oxidation in wet O.sub.2 for 15 minutes at 900.degree. C. This treatment results in silicon cones that are about 5 .mu.m high and have slightly rounded tips of diameter 25-150 nm. These silicon cones are then subjected to dry oxidation at 950.degree. C. for periods of 2-5.5 hours, followed by removal of the oxide layer on the tip. This oxidation sharpening leaves the silicon cones with atomically sharp tips having a radius of curvature of less than 1 nm. A similar process is disclosed by R. B. Marcus et al, in IEEE Trans. El. Dev., 38 (10), p. 2289 (1992), wherein the atomically sharp silicon tips are plated with tungsten and gold. The silicon tips described in these two articles are useful as electron emitters in vacuum microelectronic devices.
In Sensors and Actuators A, 34, p. 193-200 (1992), J. Brugger et al disclose a method for producing monocrystalline silicon cantilevers with integrated silicon tips. These microcantilevers are produced by micro-machining techniques. They are described as being useful as microprobes to measure friction during atomic force microscopy (AFM). This article also describes the fabrication of an array of such microprobes which enables multiple parallel or serial surface profiling to be achieved.
Similarly, T. R. Albrecht et al, in J. Vac. Sci. Tech. A, 8 (4), p. 3386 (1990), also disclose a method of fabricating sharp Si tips on microcantilevers for use in atomic force microscopy. Additionally, Park Scientific Instruments, Inc., of Sunnyvale, Calif., sells Si cantilevers with Si tips for use in atomic force microscopy, and the Nanoprobe company of Germany also sells cantilevers with Si tips for atomic force microscopy. Only the Albrech et al. device includes an actuator integrated with the cantilever, although the mechanism for actuating the cantilevers is not described.
In J. Vac. Sci. Tech. A., 8 (1), p. 317 (1990), T. Albrecht et al disclose a process for microfabricating arrays of scanning tunnelling microscopes (STM) on silicon wafers. Each scanning tunnelling microscope comprises a tunneling tip projecting from a piezoelectric actuator. The actuator is in the form of a bimorph cantilever constructed from alternating layers of multiple metallic electrodes, dielectric films, and piezoelectric zinc oxide films.
In addition to the above, W. Benecke et al, in Proc. MEMS (IEEE), Napa Valley, Calif., Feb. 11-14, 1990, disclose a silicon-based cantilever-type microactuator. The cantilever comprises a bimorph structure with an integrated heating resistor as a driving element. Similarly, R. A. Buser et al, in Sensors and Actuators, A 31, p. 29 (1992), disclose a micromachined scanning mirror having bimorph actuation. However, neither of the bimorph actuated beams in these two references has a silicon tip which projects from the beam.
Additional to the above, S. R. Weinzierl et al, in Solid State Technology, p. 31 (January 1993), and R. G. Mazur et al., in Solid State Technology (November 1981) disclose, spreading resistance probes, while M. Beily et al, in Proc. 1992 IEEE International Test Conference (1992), disclose an array probe card in the form of a very large number of probe tips made from tungsten fixed on a transparent, flexible membrane.
It can be seen from the above that a great deal of work has been done in producing microcantilevers of various shapes, structures, and compositions. However, up to the present time, no one has produced a microprobe comprising a microcantilever having a probe tip projecting from the microcantilever, wherein the microcantilever is of bimorph construction with an integrated heating element.
Accordingly, it is an object of the present invention to provide a microprobe comprising a bimorph actuated microcantilever having a probe tip which projects from the microcantilever. The probe tip may be atomically sharp or less sharp. Upon heating of the microcantilever, the probe tip comes into contact with a material to be investigated.
It is a further object of the present invention to provide a process for making such a microprobe.
It is yet another object of the present invention to incorporate an array of the inventive microprobe into an integrated probe card, wherein each of the microbes in the array can be individually addressed and actuated.
It is another object of the invention to provide multiple (2 or 4) closely-spaced tips on a single cantilever for high-resolution resistivity measurements.